The Feedback Control of Luteinizing Hormone in Normal Adult Men

Abstract

The effect of “low” and “high” constant infusion doses for 48 hr of testosterone (T), estradiol (E2), dihydrotestosterone (DHT), and 17α-hydroxyprogesterone (17-OHP) were studied in 13 normal men. Four control infusions of normal saline were performed for comparison. The slope of the line for the control studies was not statistically different from zero. Plasma T, LH, and FSH were measured, using established competitive binding or radioimmunoassay methods. Measurements were made every 6 hr during and every 12 hr following the infusion. “Low” doses of T (7 mg/day/1.7 m2) significantly (P < 0.05) suppressed LH by 50% within 48 hr in all subjects without increasing plasma T above physiological levels in blood. No significant suppression of FSH was observed at this dose. At the conclusion of the infusion, T fell below 200 ng/100 ml, and returned to baseline within 24 hr. “High” doses of T (35 mg/day/1.7 m2) significantly suppressed both LH and FSH. DHT, an androgen incapable of conversion to a known estrogen (7 mg/1.7 m2/24 hr) significantly suppressed LH by 48 hr but not FSH in all subjects studied. DHT suppression trend was less than that of testosterone. The overall effect of T could be the result either of T as an androgen, or the result of peripheral conversion to an estrogen. E2 (40 μg/day/1.7 m2) significantly reduced LH in all five studies and suppressed T within 12 hr. The effect upon LH was less than that of the testosterone infusion. The E2 infusion had no significant effect on assayable FSH levels within 48 hr unless a “high” amount (200 μg/day/1.7 m2) was given. 17α-Hydroxyprogesterone, a major testicular secretion product (2 mg/day/1.7 m2) did not lower LH or FSH. These results indicate that a dose of testosterone which mimics normal blood production rate acting either as an androgen or as an estrogen is a major factor in the control of LH.